Simon Mann, the ex-SAS soldier alleged to have led a West African coup plot, has been secretly extradited to Equatorial Guinea, his lawyer claimed yesterday.

But the precise whereabouts of the Old Etonian soldier, who disappeared from Zimbabwe's Chikurubi maximum-security prison on Wednesday, remains a mystery. One report suggested he had been moved to another prison within Zimbabwe.

The ambassador for Equatorial Guinea in London and the oil-rich state's Paris-based lawyers said they could not confirm whether Mann had been deported.

His lawyer in the Zimbabwean capital, Harare, said his client had been flown out of the country after the court dismissed an appeal against the extradition request.

Jonathan Samkange, who tried to lodge a fresh appeal, said: "They deported him at night, late Wednesday night. There are affidavits to that effect.

"The idea was that by the time we filed a notice of appeal he would have gone. This was designed to defeat the notice of our appeal. Deporting a person at night is not only mischievous but unlawful."

Mann, 54, has been held in Zimbabwe since 2004 when he met 67 mercenaries at Harare airport as they were allegedly gathering for an operation to overthrow the president of Equatorial Guinea, Teodoro Obiang Nguem. Mann has always maintained he was gathering weapons to protect a mine in Congo.

Mann - a friend and associate of Mark Thatcher, son of ex-prime minister Lady Thatcher - was sentenced to four years in prison for trying to buy weapons.

Mark Thatcher pleaded guilty in South Africa in 2005 to helping charter a helicopter he suspected "might be used for mercenary activity" in the attack.

Lord Bell, the PR adviser representing him, said yesterday: "Thatcher thinks [Mann] had not yet [left Zimbabwe] but has been moved to another jail. Mann would never have been extradited from [Britain]. It's only because of Mugabe.

"The same lawyer who was the prosecutor in the first hearing of Mann's case went on to become an appeal court judge and supreme court judge, hearing Mann's subsequent appeals ... As Simon Mann said, 'If I get sent to Equatorial Guinea, you can assume I'm dead.' But we [Britain] won't do anything about it."

It is widely believed that the extradition was a political deal. After the coup plot was foiled Obiang agreed to ship oil to Zimbabwe to help Robert Mugabe's battered economy. The two men became close allies.

If extradited to Equatorial Guinea Mann will face a fresh trial for charges of threatening the life of the head of state and threatening to overthrow the lawful government - offences that carry life sentences. The Obiang government has promised that Mann will not be executed. But his lawyers warn that conditions in the notorious Black Beach prison are unsanitary and that inmates are tortured.

One of those imprisoned for the alleged coup died in disputed circumstances. The authorities said his death was due to cerebral malaria. The South African arms dealer Nick Du Toit, a leader of the alleged coup, is there on a 34-year sentence.

Nze Nfumu Augustin, Equatorial Guinea's ambassador in London, told the Guardian: "[Mann] wasn't tried in Zimbabwe for the coup. Now the government want him to be tried for the coup attempt."

Henry Page, the Paris-based lawyer representing the west African state in civil proceedings in London, said he was trying to find out Mann's whereabouts.

The House of Lords is due to hear an appeal shortly in a case brought by Equatorial Guinea to recover damages from the alleged coup plotters based in Britain.